// Licensed to Elasticsearch B.V. under one or more contributor
// license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright
// ownership. Elasticsearch B.V. licenses this file to you under
// the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

package ucfg

import (
	"fmt"
	"reflect"
	"regexp"
	"time"
	"unicode"
	"unicode/utf8"
)

// Merge a map, a slice, a struct or another Config object into c.
//
// Merge traverses the value from recursively copying all values into a hierarchy
// of Config objects plus primitives into c.
//
// Merge supports the options: PathSep, MetaData, StructTag, VarExp, ReplaceValues, AppendValues, PrependValues
//
// Merge uses the type-dependent default encodings:
//  - Boolean values are encoded as booleans.
//  - Integer are encoded as int64 values, unsigned integer values as uint64 and
//    floats as float64 values.
//  - Strings are copied into string values.
//    If the VarExp is set, string fields will be parsed into
//    variable expansion expressions. The expression can reference any
//    other setting by absolute name.
//  - Array and slices are copied into new Config objects with index accessors only.
//  - Struct values and maps with key type string are encoded as Config objects with
//    named field accessors.
//  - Config objects will be copied and added to the current hierarchy.
//
// The `config` struct tag (configurable via StructTag option) can be used to
// set the field name and enable additional merging settings per field:
//
//  // field appears in Config as key "myName"
//  Field int `config:"myName"`
//
//  // field appears in sub-Config "mySub" as key "myName" (requires PathSep("."))
//  Field int `config:"mySub.myName"`
//
//  // field is processed as if keys are part of outer struct (type can be a
//  // struct, a slice, an array, a map or of type *Config)
//  Field map[string]interface{} `config:",inline"`
//
//  // field is ignored by Merge
//  Field string `config:",ignore"`
//
//
// Returns an error if merging fails to normalize and validate the from value.
// If duplicate setting names are detected in the input, merging fails as well.
//
// Config cannot represent cyclic structures and Merge does not handle them
// well. Passing cyclic structures to Merge will result in an infinite recursive
// loop.
func (c *Config) Merge(from interface{}, options ...Option) error {
	// from is empty in case of empty config file
	if from == nil {
		return nil
	}

	opts := makeOptions(options)
	other, err := normalize(opts, from)

	if err != nil {
		return err
	}
	return mergeConfig(opts, c, other)
}

func mergeConfig(opts *options, to, from *Config) Error {
	if err := mergeConfigDict(opts, to, from); err != nil {
		return err
	}
	return mergeConfigArr(opts, to, from)
}

func mergeConfigDict(opts *options, to, from *Config) Error {
	dict := from.fields.dict()
	if len(dict) == 0 {
		return nil
	}

	ok := false
	if opts.configValueHandling == cfgReplaceValue {
		old := to.fields.dict()
		to.fields.d = nil
		defer func() {
			if !ok {
				to.fields.d = old
			}
		}()
	}

	for k, v := range dict {
		ctx := context{
			parent: cfgSub{to},
			field:  k,
		}

		old, _ := to.fields.get(k)
		opts, err := fieldOptsOverride(opts, k, -1)
		if err != nil {
			return err
		}
		merged, err := mergeValues(opts, old, v)
		if err != nil {
			return err
		}

		to.fields.set(k, merged.cpy(ctx))
	}

	ok = true
	return nil
}

func mergeConfigArr(opts *options, to, from *Config) Error {
	currHandling := opts.configValueHandling
	opts, err := fieldOptsOverride(opts, "*", -1)
	if err != nil {
		return err
	}
	switch currHandling {
	case cfgReplaceValue:
		return mergeConfigReplaceArr(opts, to, from)

	case cfgArrPrepend:
		return mergeConfigPrependArr(opts, to, from)

	case cfgArrAppend:
		return mergeConfigAppendArr(opts, to, from)

	case cfgDefaultHandling, cfgMergeValues:
		return mergeConfigMergeArr(opts, to, from)
	default:
		return mergeConfigMergeArr(opts, to, from)
	}
}

func mergeConfigReplaceArr(opts *options, to, from *Config) Error {
	a := from.fields.array()
	if len(a) == 0 {
		return nil
	}

	var parent value = cfgSub{to}
	var fields = fields{
		d: to.fields.d,
		a: make([]value, 0, len(a)),
	}
	fields.append(parent, a)
	*to.fields = fields
	return nil
}

func mergeConfigMergeArr(opts *options, to, from *Config) Error {
	l := len(to.fields.array())
	arr := from.fields.array()
	if l > len(arr) {
		l = len(arr)
	}

	var parent value = cfgSub{to}

	// merge array indexes available in to and from
	for i := 0; i < l; i++ {
		ctx := context{
			parent: parent,
			field:  fmt.Sprintf("%v", i),
		}

		// possible for individual index to be replaced
		idxOpts, err := fieldOptsOverride(opts, "", i)
		if err != nil {
			return err
		}
		old := to.fields.array()[i]
		merged, err := mergeValues(idxOpts, old, arr[i])
		if err != nil {
			return err
		}
		to.fields.setAt(i, parent, merged.cpy(ctx))
	}

	if len(arr) > l {
		// add additional array entries not yet in 'to'
		to.fields.append(parent, arr[l:])
	}
	return nil
}

func mergeConfigPrependArr(opts *options, to, from *Config) Error {
	a1 := to.fields.array()
	a2 := from.fields.array()
	if len(a2) == 0 {
		return nil
	}

	var parent value = cfgSub{to}
	var fields = fields{
		d: to.fields.d,
		a: make([]value, 0, len(a1)+len(a2)),
	}
	fields.append(parent, a2)
	fields.append(parent, a1)
	*to.fields = fields
	return nil
}

func mergeConfigAppendArr(opts *options, to, from *Config) Error {
	to.fields.append(cfgSub{to}, from.fields.array())
	return nil
}

func mergeValues(opts *options, old, v value) (value, Error) {
	if old == nil {
		return v, nil
	}

	// check if new and old value evaluate to sub-configurations. If one is no
	// sub-configuration, use new value only.
	subOld, err := old.toConfig(opts)
	if err != nil {
		return v, nil
	}
	subV, err := v.toConfig(opts)
	if err != nil {
		return v, nil
	}

	// merge new and old evaluated sub-configurations and return subOld for
	// reassigning to old key in case of subOld being generated dynamically
	if err := mergeConfig(opts, subOld, subV); err != nil {
		return nil, err
	}
	return cfgSub{subOld}, nil
}

// convert from into normalized *Config checking for errors
// before merging generated(normalized) config with current config
func normalize(opts *options, from interface{}) (*Config, Error) {
	vFrom := chaseValue(reflect.ValueOf(from))

	switch vFrom.Type() {
	case tConfig:
		return vFrom.Addr().Interface().(*Config), nil
	case tConfigMap:
		return normalizeMap(opts, vFrom)
	default:
		// try to convert vFrom into Config (rebranding)
		if v, ok := tryTConfig(vFrom); ok {
			return v.Addr().Interface().(*Config), nil
		}

		// normalize given map/struct value
		switch vFrom.Kind() {
		case reflect.Struct:
			return normalizeStruct(opts, vFrom)
		case reflect.Map:
			return normalizeMap(opts, vFrom)
		case reflect.Array, reflect.Slice:
			tmp, err := normalizeArray(opts, tagOptions{}, context{}, vFrom)
			if err != nil {
				return nil, err
			}
			c, _ := tmp.toConfig(opts)
			return c, nil
		}

	}

	return nil, raiseInvalidTopLevelType(from, opts.meta)
}

func normalizeMap(opts *options, from reflect.Value) (*Config, Error) {
	cfg := New()
	cfg.metadata = opts.meta
	if err := normalizeMapInto(cfg, opts, from); err != nil {
		return nil, err
	}
	return cfg, nil
}

func normalizeMapInto(cfg *Config, opts *options, from reflect.Value) Error {
	k := from.Type().Key().Kind()
	if k != reflect.String && k != reflect.Interface {
		return raiseKeyInvalidTypeMerge(cfg, from.Type())
	}

	for _, k := range from.MapKeys() {
		k = chaseValueInterfaces(k)
		if k.Kind() != reflect.String {
			return raiseKeyInvalidTypeMerge(cfg, from.Type())
		}

		err := normalizeSetField(cfg, opts, noTagOpts, k.String(), from.MapIndex(k))
		if err != nil {
			return err
		}
	}
	return nil
}

func normalizeStruct(opts *options, from reflect.Value) (*Config, Error) {
	cfg := New()
	cfg.metadata = opts.meta
	if err := normalizeStructInto(cfg, opts, from); err != nil {
		return nil, err
	}
	return cfg, nil
}

func normalizeStructInto(cfg *Config, opts *options, from reflect.Value) Error {
	v := chaseValue(from)
	numField := v.NumField()

	for i := 0; i < numField; i++ {
		var err Error
		stField := v.Type().Field(i)

		// ignore non exported fields
		if rune, _ := utf8.DecodeRuneInString(stField.Name); !unicode.IsUpper(rune) {
			continue
		}

		name, tagOpts := parseTags(stField.Tag.Get(opts.tag))
		if tagOpts.ignore {
			continue
		}

		if tagOpts.squash {
			vField := chaseValue(v.Field(i))
			switch vField.Kind() {
			case reflect.Struct:
				err = normalizeStructInto(cfg, opts, vField)
			case reflect.Map:
				err = normalizeMapInto(cfg, opts, vField)
			default:
				return raiseSquashNeedsObject(cfg, opts, stField.Name, vField.Type())
			}
		} else {
			name = fieldName(name, stField.Name)
			err = normalizeSetField(cfg, opts, tagOpts, name, v.Field(i))
		}

		if err != nil {
			return err
		}
	}
	return nil
}

func normalizeSetField(
	cfg *Config,
	opts *options,
	tagOpts tagOptions,
	name string,
	v reflect.Value,
) Error {
	val, err := normalizeValue(opts, tagOpts, context{}, v)
	if err != nil {
		return err
	}

	p := parsePath(name, opts.pathSep)
	old, err := p.GetValue(cfg, opts)
	if err != nil {
		if err.Reason() != ErrMissing {
			return err
		}
		old = nil
	}

	switch {
	case !isNil(old) && isNil(val):
		return nil
	case isNil(old):
		return p.SetValue(cfg, opts, val)
	case isSub(old) && isSub(val):
		cfgOld, _ := old.toConfig(opts)
		cfgVal, _ := val.toConfig(opts)
		return mergeConfig(opts, cfgOld, cfgVal)
	default:
		return raiseDuplicateKey(cfg, name)
	}
}

func normalizeStructValue(opts *options, ctx context, from reflect.Value) (value, Error) {
	sub, err := normalizeStruct(opts, from)
	if err != nil {
		return nil, err
	}
	v := cfgSub{sub}
	v.SetContext(ctx)
	return v, nil
}

func normalizeMapValue(opts *options, ctx context, from reflect.Value) (value, Error) {
	sub, err := normalizeMap(opts, from)
	if err != nil {
		return nil, err
	}
	v := cfgSub{sub}
	v.SetContext(ctx)
	return v, nil
}

func normalizeArray(
	opts *options,
	tagOpts tagOptions,
	ctx context,
	v reflect.Value,
) (value, Error) {
	l := v.Len()
	out := make([]value, 0, l)

	cfg := New()
	cfg.metadata = opts.meta
	cfg.ctx = ctx
	val := cfgSub{cfg}

	for i := 0; i < l; i++ {
		idx := fmt.Sprintf("%v", i)
		ctx := context{
			parent: val,
			field:  idx,
		}
		tmp, err := normalizeValue(opts, tagOpts, ctx, v.Index(i))
		if err != nil {
			return nil, err
		}
		out = append(out, tmp)
	}

	cfg.fields.a = out
	return val, nil
}

func normalizeValue(
	opts *options,
	tagOpts tagOptions,
	ctx context,
	v reflect.Value,
) (value, Error) {
	v = chaseValue(v)

	switch v.Type() {
	case tDuration:
		d := v.Interface().(time.Duration)
		return newString(ctx, opts.meta, d.String()), nil
	case tRegexp:
		r := v.Addr().Interface().(*regexp.Regexp)
		return newString(ctx, opts.meta, r.String()), nil
	}

	// handle primitives
	switch v.Kind() {
	case reflect.Bool:
		return newBool(ctx, opts.meta, v.Bool()), nil
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		i := v.Int()
		if i > 0 {
			return newUint(ctx, opts.meta, uint64(i)), nil
		}
		return newInt(ctx, opts.meta, i), nil
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		return newUint(ctx, opts.meta, v.Uint()), nil
	case reflect.Float32, reflect.Float64:
		f := v.Float()
		return newFloat(ctx, opts.meta, f), nil
	case reflect.String:
		return normalizeString(ctx, opts, v.String())
	case reflect.Array, reflect.Slice:
		return normalizeArray(opts, tagOpts, ctx, v)
	case reflect.Map:
		return normalizeMapValue(opts, ctx, v)
	case reflect.Struct:
		if v, ok := tryTConfig(v); ok {
			c := v.Addr().Interface().(*Config)
			ret := cfgSub{c}
			if ret.Context().parent != ctx.parent {
				ret.SetContext(ctx)
			}
			return ret, nil
		}

		return normalizeStructValue(opts, ctx, v)
	default:
		if v.IsNil() {
			return &cfgNil{cfgPrimitive{ctx, opts.meta}}, nil
		}
		return nil, raiseUnsupportedInputType(ctx, opts.meta, v)
	}
}

func normalizeString(ctx context, opts *options, str string) (value, Error) {
	if !opts.varexp {
		return newString(ctx, opts.meta, str), nil
	}

	varexp, err := parseSplice(str, opts.pathSep)
	if err != nil {
		return nil, raiseParseSplice(ctx, opts.meta, err)
	}

	switch p := varexp.(type) {
	case constExp:
		return newString(ctx, opts.meta, string(p)), nil
	case *reference:
		return newRef(ctx, opts.meta, p), nil
	}

	return newSplice(ctx, opts.meta, varexp), nil
}

func fieldOptsOverride(opts *options, fieldName string, idx int) (*options, Error) {
	if opts.fieldHandlingTree == nil {
		return opts, nil
	}
	cfgHandling, child, ok := opts.fieldHandlingTree.fieldHandling(fieldName, idx)
	child, err := includeWildcard(child, opts.fieldHandlingTree)
	if err != nil {
		return nil, err
	}
	if !ok {
		// Only return a new `options` when arriving at new nested child. This
		// combined with optimizations in `includeWildcard` will ensure that only
		// a new opts will be created and returned when absolutely required.
		if child != nil && opts.fieldHandlingTree != child {
			newOpts := *opts
			newOpts.fieldHandlingTree = child
			opts = &newOpts
		}
		return opts, nil
	}
	// Only return a new `options` if absolutely required.
	if opts.configValueHandling != cfgHandling || opts.fieldHandlingTree != child {
		newOpts := *opts
		newOpts.configValueHandling = cfgHandling
		newOpts.fieldHandlingTree = child
		opts = &newOpts
	}
	return opts, nil
}

func includeWildcard(child *fieldHandlingTree, parent *fieldHandlingTree) (*fieldHandlingTree, Error) {
	if parent == nil {
		return child, nil
	}
	wildcard, err := parent.wildcard()
	if err != nil {
		return child, nil
	}
	if child == nil && len(parent.fields.dict()) == 1 {
		// parent is already config with just wildcard
		return parent, nil
	}
	sub := newFieldHandlingTree()
	if child != nil {
		if err := sub.merge(child); err != nil {
			return nil, err.(Error)
		}
	}
	if err := sub.setWildcard(wildcard); err != nil {
		return nil, err.(Error)
	}
	return sub, nil
}
